Future telecommunication is characterized by an ever increasing part of nonverbal services. Intermittent traffic volume is characteristic of nonverbal services. The transmission capacity required for such services is therefore not constant. Video transmissions occupy a certain intermediate position. The starting point is the analog video signal, which is periodically scanned and converted into a digital signal with constant data flow. Aside from the television-radio service, in which no digitalization takes place, the very high traffic volume of video signals is not accepted. For that reason, the redundancy contained in such signals is reduced to a greater or lesser degree by means of "videocodecs". The greater the reduction of redundancies, the less constant is the traffic volume. The reduction of redundancies also plays a role in voice transmission by radio. Voice pauses can be recognized and no signal is transmitted during such voice pauses.
An expanded solution for the transmission of signals with variable traffic volume consists of separating the total capacity of a transmission channel into equally long sections (time slots, cells), and utilizing more or less of these sections for a single transmission. The remaining sections are either used in the time multiplex for other transmissions, are filled with blank information, or they are not used. Examples are the multiple access to telecommunication satellites with the Time Division Multiple Access (TDMA), or the Asynchronous Transfer Mode (ATM) in broad-band networks.
The disadvantages of this solution are greater interference occurring, above all during radio traffic, which is due to the time compression; the greater expense for synchronization in radio networks, in which different running times must also be taken into consideration; and sharp limitation of the total capacity. Even if a lower transmission quality is accepted, the total capacity of a transmission medium can only be increased at great expense.